The field of application of the invention comprises wrist-worn devices, such as heart rate monitors, watches, wrist computers, or the like. The invention particularly relates to the illumination of a display on the wrist-worn device in question.
One important, and almost indispensable, characteristic of wrist-worn, watch-like devices, such as wrist watches, heart rate monitors and wrist computers, is the possibility to use the device in low ambient light and no ambient light conditions. The heart rate monitor to be described as an example is a device used in sports and exercising which incorporates the possibility to measure the user""s hear rate information during physical exercise. The structure of some known heart rate monitors comprises an electrode belt to be positioned on the chest to measure heart rate information from an electric signal caused by the heart and to transmit the heart rate information to a device carried on the wrist which then shows the heart rate on its display. In conditions of low ambient light the display can be illuminated by pressing a push-button on the wrist-worn device, whereby the display is illuminated by electroluminescence or by light emitted from a light source, such as a LED (Light Emitting Diode). In prior art LED illumination solutions one or more light sources are arranged close to the background plate to allow as much of the light energy emitted by the LED as possible to be used for illuminating the background plate. In a known solution the light emitted from the light source is directed by means of lenses. In prior art solutions, the background plate is an injection-moulded, 1 mm thick plastic plate, for example. During its manufacture, the background plate is provided with macrostructures, for example projections, for directing light to the display. In addition to macrostructures, another attempt to improve the directing of light to the display is to manufacture the background plate such that its becomes gradually thinner further away from the LED.
The prior art solution for illuminating the background plate of a heart rate monitor involves a significant drawback in that a major portion of the directed light energy misses the background plate, thereby causing significant light energy losses.
It is an object of the invention to provide an improved method and equipment implementing the method for illuminating a background plate of a display on a wrist-worn device. This is achieved with the method to be described below, which is a method for illuminating a background plate of a display on a wrist-worn device. The method employs a light source for emitting light to a guide chamber at least partly surrounding the light source for collecting the light and for directing it to the background plate.
The invention further relates to a wrist-worn device comprising a background plate to be illuminated for the display of the wrist-worn device and a light source for illuminating the background plate. The wrist-worn device comprises a guide chamber at least partly surrounding the light source for collecting light emitted from the light source and for directing it to the background plate.
The preferred embodiments of the invention are disclosed in the dependent claims.
As already stated, the invention relates to a method and equipment for illuminating the background plate of a display on a wrist-worn device. In this specification, xe2x80x98wrist-worn devicexe2x80x99 refers to watches, heart rate monitors, wrist computers, or similar devices carried on the wrist. xe2x80x98Heart rate monitorxe2x80x99 is here defined as a device the functions of which comprise at least a function for measuring heart rate, i.e. heartbeat. xe2x80x98Wrist computerxe2x80x99 in turn can be defined for example as a device the functions of which comprise at least a function for locating the user. Further, in this specification, xe2x80x98displayxe2x80x99 refers to those parts of a device which are used for visually displaying the information produced by the wrist-worn device to the user of the device. The display therefore comprises for example a background plate to be illuminated, a liquid crystal display and a plastic shield protecting the liquid crystal display and allowing it to be viewed. The wrist-worn device of the invention comprises a guide chamber for collecting light and for directing it from the light source to the background plate. In the solution of the invention, the guide chamber surrounds the light source at least partly, thus allowing light to be optimally collected from the light source. In this context, the term xe2x80x98surroundingxe2x80x99 means that the light source is at least partly inside the space defined by the guide chamber. The method of the invention differs for example from prior art solutions implemented by means of a lens, where the lens is used for directing light energy, but, since there is no collecting function, the loss of energy is significant. The solution of the invention is not restricted to the number of light sources or guide chambers the wrist-worn device comprises.
In a wrist-worn device of a preferred embodiment of the invention the background plate to be illuminated and the one or more guiding chambers form a single, uniform piece, which is advantageous from the point of view of the manufacturing process. Consequently, in one preferred embodiment, the cross-section of the guide chamber is substantially equal in thickness with the background plate. However, the invention is not restricted to a guide chamber and background plate made of one and the same piece, but it is possible that the guide chamber is manufactured separately and then attached to the background plate. In another preferred embodiment, the guide chamber and the background plate are interconnected, i.e. they are joined together. This allows to minimize any losses of light energy caused during the transmission of light. In another preferred embodiment the guide chamber and the background plate are made of a film-like material, as distinct from pieces manufactured by injection moulding, for example. Thin, film-like material is significantly easier to form into the shape required by the guide chamber than pieces made by injection moulding.
In a preferred embodiment, the guide chamber comprises a guide surface on its inner surface, the guide surface being in the area between a first end and second end that the guide chamber comprises. The guide surface is preferably circular. In a preferred embodiment, the guide surface is conical, the diameter of the cross-section of the first end thus being greater than that of the cross-section of the second end. The conical guide chamber is preferably open at its first end and closed at its second end. The guide surface between the first end and the second end preferably defines an open inner space, i.e. the guide means of this embodiment is not a closed plastic cone, for example. The light source is preferably arranged to be at least partly inside the guide means, the numerical aperture of the light source being directed towards the second, i.e. closed end of the cone. Preferably all the light emitted to the numerical aperture by the light source is collected inside the area encircled by the first end of the guide chamber.
According to a second preferred embodiment the guide chamber is shaped like a roll, the diameters of the cross-sections of the first end and the second end of the guide chamber thus being substantially equal. The light source is preferably arranged inside the guide chamber, on the inner surface side thereof, and directed with regard to the roll-shaped guide chamber such that as much of the light emitted by the light source as possible is directed to the wall of the guide chamber, i.e. to the guide surface. This is achieved for example by placing the light source obliquely with respect to the roll-shaped guide chamber. It is apparent that the above-described conical and roll-shaped forms of the guide chamber only serve as examples, the invention not being restricted to them. The inventive idea of the present application also comprises other guide chamber shapes.
The guide chamber of a preferred embodiment comprises at least one guide means for directing light from the guide chamber to the background plate. The guide means is for example a mirror, prism, air bubble, or a similar means causing light to be reflected or refracted. The guide chamber preferably comprises a plural number of guide means meant to make light propagate to the background plate as a uniform flow of light. The guide members are placed either on the guide surface or inside the guide chamber material. In a preferred embodiment, the flow of light directed using the guiding means propagates inside the background material. In another preferred embodiment the flow of light propagates along the surface of the background plate, the guiding chamber and the background plate being provided with a gap between them to allow the light to propagate towards the background plate. The background plate preferably comprises diffractive elements for reflecting the light received from the guide chamber or for directing it substantially perpendicularly with regard to the background plate towards the shield on the wrist-worn device""s display.
The wrist-worn device preferably employs a LED as a light source, although other light sources producing optical power can also be used. The guide chamber and the background plate are made of at least partly light conducting material, such as plastic or glass. The background plate preferably conducts light well enough to allow at least some of the light produced by the light source to reach the far side of the background plate when seen from the light source.
The method of the invention defines the steps to be taken to illuminate the background plate of the display of the above-described wrist-worn device of the invention by using a light source and a guide chamber.
An advantage of the invention is that, compared with prior art solutions, it allows the light energy emitted by the light source to be more efficiently used for illuminating the background plate.